Now that a large number of people are at least partially vaccinated in the U.S. and COVID is on a downswing, the question has turned from whether vaccines work to how long they work and how well they will continue to work against variants. There are also questions about natural immunity and how long it lasts. In order to begin to understand the answers to these questions, we have to understand the building blocks of immunity, the types of immunity, and how immunity works.
Building Blocks of Immunity
There are many important components of an immune response, but I’m focusing on three components in this post – B-cells, T-cells, and macrophages. The description of the components and their processes is very simplified in this post, but the references linked throughout the post and at the end can provide more in-depth information about immunity.
B-cells protect against antigens (viruses, bacteria, and other foreign elements) by producing antibodies, and B-cells also clean up after T-cells do their job. Antibodies are proteins in the blood that find specific antigens and attack them. Ghose (2020) describes the shape of antibodies and the different types of antibodies. The antibodies clump the antigens together, stopping them from infecting your cells and allowing macrophages to find and clean up the infection. B-cells, and by extension antibodies, work to stop antigens from entering the cells.
If an antigen gets past the antibodies and infects a cell, the T-cells get to work fighting the infected cells. T-cells circulate in the blood until the specific antigen they attack is present in a cell. When the antigen is detected, the T-cells attack. Ryding (2021) explains that in children, T-cells are plentiful and they begin to build up a memory as the body comes in contact with new antigens it hasn’t experienced before. As the body ages, the T-cells help maintain homeostasis and protect against antigens. Later in life, T-cells decrease which makes the body vulnerable to infections.
Types of Immunity
We naturally have three types of immunity: innate, adaptive, and passive. Innate immunity is immunity we’re born with. Hirsch (2019) explains this as the skin protecting us against foreign invaders, and also the body recognizing when something is foreign and could be dangerous. Adaptive immunity applies to the building blocks discussed earlier – the body learns what it must protect against by exposure throughout the lifetime, and it adapts. Vaccines and infections trigger an adaptive immune response, allowing the body to remember the antigen so the B-cells and the T-cells can prepare to fight the antigen in the future. Hirsch (2019) explains the third type of immunity, passive immunity, is short-term, and is “borrowed” from someone else; for example, a breastfeeding baby has temporary immunity against certain antigens thanks to its mother’s milk.
Herd immunity is another type of immunity, and this occurs when a large enough percentage of a population develops immunity to a disease to prevent the spread of the disease. When we have achieved herd immunity, everyone, including people who have not developed immunity to an antigen, are protected from infection. This has been the goal with COVID vaccine uptake.
Immunity Doesn’t Always Mean Preventing Infection
It’s important to understand that immunity is not always the same as preventing infection. You can develop immunity and still get infected.
Caddy (2021) tells readers some vaccines prevent symptomatic disease while others completely prevent infection. When a vaccine completely prevents infection, that’s called sterilizing immunity, and you will have neutralizing antibodies present. A vaccine that doesn’t provide sterilizing immunity means you can still catch the disease and possibly spread it, but you won’t get sick. Caddy adds it’s “extremely difficult” to produce vaccines that provide sterilizing immunity. McKenna (2021) explains some vaccines widely used today, such as measles, provide sterilizing immunity while others, such as hepatitis B, provide immunity but not sterilizing immunity. But McKenna adds sterilizing immunity isn’t necessary to curb infections, including COVID, because vaccines that do not have sterilizing immunity still reduce an infected person’s viral load. A decreased viral load will help decrease disease transmission. McKenna’s article explains other diseases and vaccines and how these vaccines prevent infection.
Presence of Antibodies and Immunity
In its website about coronavirus immunity, the University of Maryland Medical System (2021) stresses that the presence of antibodies doesn’t mean you are immune to a disease; it means you have been infected with the virus at some point and your body fought it. Also, because antibodies decline over time, lack of antibodies doesn’t mean you don’t have immunity against a disease (Poltorak, 2020). The key to immunity lies in the entire immune system response, including the memory of the B-cells and T-cells. That must be studied over time, and that long-term study helps the medical community determine when boosters of routine vaccinations are necessary.
Currently with COVID, we can only say the immune response appears to be active for X amount of time because that’s all the amount of time we’ve had to study this novel virus. So when you hear news reports that say things like, “Vaccine immunity lasts 6 months,” it doesn’t mean it only lasts 6 months and you will need to get re-vaccinated every 6 months. It just means 6 months is all the data they have, so they can’t say for certain it will last longer even if it looks promising.
Lasting Immunity and Variant Protection
In April 2021, it was determined that immunity from vaccines lasted six months and would likely last longer (Curley, 2021). Fortunately, at the time of this posting, the immune response seems to remain strong in patients who have recovered in COVID and still remains strong in those vaccinated. In January 2021, the NIH determined that 95% of people who recovered from COVID had “durable memories of the virus up to eight months after infection.” Ries (2021) also points to evidence of low rates of reinfection for those who recovered from COVID. Finally, Mandavalli (2021) discusses new research that suggest immune response from the mRNA vaccines could last years without a booster.
The vaccines also continue to be effective against variants at the time of this posting. A study by Alter, Yu, and Barouch (2021) published in Nature show the Johhson & Johnson vaccines are protecting against troubling COVID variants for various reasons. Palca (2021) spoke to Barouch to break down the findings for the public. Barouch (as cited in Palca, 2021) explains that although neutralizing antibodies, which prevent a virus from entering cells, are reduced when you measure the J&J vaccine against the South African (now called the Beta) variant, the T-cells are not reduced. The T-cells, specifically the CD8 or killer T-cells, stop a virus from spreading uncontrollably. These cells attack the infection, and they were not reduced at all with the Beta variant. Other studies have replicated this result with Pfizer and Moderna vaccines and variants. It’s still unclear how long theT-cell response lasts, but that’s being investigated.
Learn More
Check out these resources for additional information on immunity and the immune system.
- Antibodies and adaptive immune system
- B-cells
- B-cells and T-cells
- How vaccines work
- Immune response
- T-cells
- T-cells and COVID
Christina J. Steffy 
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